Designing RF circuits for Internet of Things (IoT) applications has been focused on short range communication. There are several applications, however, where sensor nodes would benefit from having longer range, while still maintaining the qualities of the short range radios. Such a sensor node would not have the size constraint that body area networks impose and therefore more aggressive energy harvesting can be used which allows for a larger power budget. Many commercial companies are making long range communication chips for IoT including Analog Devices, Texas Instruments, and Semtech.
Long range radios would be useful in many different scenarios. A simple example would be for remote environmental sensing applications that do not require high data rates and may need to communicate once in a while. For example, Analog Devices introduced the CN0164 Low Power, Long Range ISM Wireless Measuring Node. This system consists of a low power temperature measurement node that wakes once a minute, measures the temperature, transmits the information, then returns to sleep.
However, it will be difficult to operate any of the mentioned radios off harvested energy supplies. Using the Texas Instruments CC1101 as an example, assume the average power for the sensor node is required to be 50 μW. The CC1101 can be configured to communicate at 1 kbps and consumes 48 mW in receive mode and 48 mW in transmit mode. Duty cycling to make the average power 50 μW would lead to an average data rate of only 1.04 bps, which is optimistic because it does not take into account startup time. If the sensor node has to transmit a 100-bit packet at 1 kbps then 1.6 mF of storage capacitance is required in order to prevent the supply voltage from dropping more than 1V.
This disclosure presents a long range transceiver (LRTRx) design that runs on harvested energy effectively. An average power consumption of 50 μW is achievable and the instantaneous power should be kept below 1 mW for receive and a few mW for transmit.
This section provides background information related to the present disclosure which is not necessarily prior art.